The invention relates to actuators of flaps for distribution or mixing of air or for recirculation (air intake) in motor-vehicle air-conditioning installations.
In such installations, the flaps are moved by geared-down motors in response to actuation commands produced by a central control unit on the basis of the requirements to be satisfied, such as starting or stopping of ventilation, adjustment of ambient temperature, demisting, deicing, etc.
Whether it is to respond as rapidly as possible to the requirements, or to cope with particular situations, for example detection of pollution, it is desirable to shift the flaps so as to bring them into the desired position in the shortest possible time.
To that end, the geared-down motors, generally stepper motors, are chosen to deliver the necessary power to drive the flaps at maximum speed under all circumstances, that is to say whatever the fluctuations in the power-supply voltage and the requirements in terms of torque. The torque requirements are variable not only on the basis of the technology of the flaps and of the nature of their drive kinematics, but also on the basis of instantaneous conditions, such as ventilation power, back-pressure exerted on the flap and acting in opposition to the desired movement, temperature, etc.
The geared-down motors used in the known air-conditioning installations are therefore over-dimensioned in terms of power in order to satisfy the torque requirements.
The object of the invention is to allow the use of geared-down motors of lower power than those habitually used nowadays, so as to reduce the costs of the air-conditioning installations, but while satisfying the torque requirements and without substantially penalising the speed of execution of the actuation commands.
This object is achieved, in accordance with the invention, by a method of control of an actuator stepper motor according to which, during the actuation of the flap, the drive frequency of the stepper motor is adapted to the requirements for torque delivered by the motor for shifting the flap.
The adaptation of the drive frequency can be achieved by continuously gathering information representing the requirements for torque delivered by the motor in order to shift the flap, the drive frequency being reduced, if appropriate, in response to a detected increase in the torque requirements and, when the drive frequency is below a predetermined maximum frequency, the drive frequency being increased, if appropriate, in response to a detected reduction in the torque requirements.
Advantageously, in response to an actuation command, the operation of the stepper motor is initially ordered at the predetermined maximum frequency.
The variation in the drive frequency can be achieved in a practically continuous way on the basis of the fluctuations in the detected-torque requirements, or in steps, the change from one step to another being ordered in response to the crossing of a threshold by the detected-torque requirements.
By modulating the drive frequency, as appropriate, and thus the speed of the stepper motor on the basis of the torque requirements, the method according to the invention makes it possible to optimise the use of the available power. An over-dimensioning of the power, as would be necessary to deal with peaks in torque requirements during transient periods within the phase of movement of the flaps, becomes pointless. Any such transient periods rarely represent more than 20% of the total time of actuation of the flaps, such that the slowing of the motor during any such transient periods does not substantially affect the total duration of the actuation.
With the duration of actuation being restricted, it is possible, without risk of excessive heating, to make the stepper motor function in over-powered mode, by application of a power-supply voltage corresponding to a mode of operation with excess power. By way of safety, it is then possible to cause stopping of the motor if a heating-limit temperature is exceeded.
The detection of the requirements for torque delivered by the motor can be made by measuring a quantity directly or indirectly representative of the torque, such as a voltage measurement on one phase of the motor, a measurement of the current in a winding of the motor or measurement of the instantaneous rotational speed of the motor, a slowing below a certain limit, in this latter case, signifying the crossing of a torque-value threshold for the drive frequency used.
A further object of the invention is to provide an actuator allowing implementation of the method defined above.
This object is achieved by virtue of a flap actuator comprising a stepper motor for driving the flap, an electrical power-supply circuit for the motor, a control input and a control unit linked to the control input and to the electrical power-supply circuit for delivering to the stepper motor a power-supply voltage at a given frequency in response to an actuation command received on the control input, an actuator in which, in accordance with the invention:
means are provided for supplying the control unit with information representing the torque requirements which the motor has to deliver in order to shift the flap, and
the control unit comprises means for adapting the drive frequency of the stepper motor on the basis of the said information representing the torque requirements.
A further subject of the invention is a vehicle air-conditioning installation comprising at least one actuator.